Many microsurgical procedures require precision cutting, removal, and/or separation of various body tissues. For example, certain ophthalmic surgical procedures require the cutting and/or removal of the vitreous humor, a transparent jelly-like material that fills the posterior segment of the eye. The vitreous humor, or vitreous, is composed of numerous microscopic fibrils that are often attached to the retina by the posterior vitreous cortex. Therefore, cutting and removal of the vitreous must be done with great care to avoid traction on the retina, the separation of the retina from the retinal pigment epithelium, a retinal tear, or, in the worst case, retinal detachment. Delicate operations such as mobile tissue management (e.g., cutting and removal of vitreous near a detached portion of the retina or a retinal tear), vitreous base dissection, and cutting and removal of membranes are particularly difficult.
With age, the vitreous may naturally contract and separate from the retina and, generally, this occurs without negatively affecting the vision or health of a person's eyes. However, in some instances the vitreous may detach from some portions of the retina without detaching from others. This may cause a contracting vitreous to pull on the retina, distorting vision and potentially causing a tear also called a retina break, potentially leading to retinal detachment. Other conditions such as vitreomacular traction, resulting from the vitreomacular adhesion and vitreomacular schisis are a result of incomplete separation of the vitreous humor from the posterior retina. The condition may be treated by attempting to mechanically detach the adhered portion of the vitreous from the retina.
Detaching adherent vitreous can be accomplished using standard vitrectomy probes. These typically include a hollow needle with a port on the end to pull in fibrils forming the vitreous humor. An inner member, placed within the hollow needle, moves back and forth to open and close the port. This operates to cut any fibrils that enter the port while it is open. The motion used to position vitreous within the hollow needle may be a back and force motion tangential to the surface of the retina that places significant sheer stress on the delicate retina through the posterior vitreous cortex. Another approach relies on enzymes to chemically separate the vitreous from the retina. While this approach may be effective, it may also generate unwanted side effects. Accordingly, the current approaches are not satisfactory in all respects.